The aims of this project are to learn how lymphocyte cells interact with molecules, both foreign to the body and thus acting as vaccine substances or antigens, and molecules of the body's own tissues, known as self antigens. This encounter between lymphocyte cells, in health, leads to appropriate defense responses in the first case but to a lack of such in the second. Understanding these contrasting roles of antigens, that is, immune activation and tolerance induction, is one of the central unsolved problems of immunology. Solution of the puzzle will be directly relevant not only to the construction of better and also new vaccines, but also to better understanding of, and control over, autoimmune diseases and problems in organ transplantation. The methods for achieving this understanding will involve culturing single B lymphocytes that have been specially prepared from normal mouse spleen to be reactive to (and bear receptors for) one particular antigen. The cells will be stimulated with that antigen and with purified growth and differentiation factors active on B lymphocytes. Moreover, both antigens and lymphocytes will be classified into new functional subsets through this technology, which is novel because it avoids the need to have present in the culture other, irrelevant cells, which obscure microscopic visualization of immune proliferation and the interpretation of cellular events. The new cloning methods will be applied also to cells that have been made tolerant either in vivo or in vitro in order to determine why tolerant cells fail to respond. The same basic approach of novel cloning technologies will be applied to T lymphocytes to develop clearer insights into the collaboration between T and B cells that leads to antibody production.